Electron Push–Pull Effects in 3,9-Bis(<i>p</i>-(R)-diphenylamino)perylene and Constraint on Emission Color Tuning

Abstract

A series of perylene-based donor–acceptor–donor (D–A–D) compounds, 3,9-bis(p-(R)-diphenylamino)perylene (R: CN (2a), F (2b), H (2c), Me (2d), and OMe (2e)), was synthesized using 3,9-dibromoperylene with p-(R)-diphenylamine, and the intramolecular charge transfer (ICT) on the D–A–D system with regard to the electron push–pull substituent effect was investigated. By introducing various p-(R)-diphenylamine derivatives with electron-donating or electron-withdrawing R groups, the energy band gaps of the D–A–D compounds were systematically controlled and the emission colors were efficiently tuned from green to red. As expected, the steady state emission spectra of all D–A–D compounds were observed, as well as the emission color controlled, depending on the Hammett substituent constants (σp). In the Lippert–Mataga plots, a different charge-transfer character was observed depending on the electron push–pull substitution, which showed gradually increased ICT characters from the electron-withdrawing to donating substitution. However, exceptionally, the strong electron-withdrawing group of CN-substituted 2a did not correlate with the other R group compounds. From the experimental data and density functional theory calculations, we assume that there is a constraint on emission color tuning to generate higher energy of blue emission in the D–A–D molecular system, due to the reverse charge-transfer property caused by the strong electron-withdrawing group.